1. Field of the Invention
The present invention relates to a method of controlling an electromagnetic valve unit for use in internal combustion engines.
2. Description of the Related Art
Heretofore, there have been known electromagnetic valve units for selectively opening and closing intake or exhaust valves in the cylinders of internal combustion engines. A basic structure of such an electromagnetic valve unit is shown in FIG. 1 of the accompanying drawings.
As shown in FIG. 1, the electromagnetic valve unit has a valve head 3 for selectively opening and closing an intake or exhaust port 2 (hereinafter referred to as xe2x80x9cintake/exhaust port 2xe2x80x9d) of a combustion chamber 1 of each cylinder of an internal combustion engine. The valve head 3 is mounted on an end of a shank 3a, and an armature 4 in the form of an iron disk is attached to the other end of the shank 3a. The shank 3a is axially reciprocally, i.e., vertically in FIG. 1, movable to move the valve head 3 between a closed position, indicated by the imaginary lines, for closing the intake/exhaust port 2 and an open position, indicated by the imaginary lines, for opening the intake/exhaust port 2.
Some electromagnetic valve units include a drive rod (not shown) held coaxially against the upper end of a valve stem for movement in union with the valve stem, and an armature attached to the drive rod. In such electromagnetic valve units, the valve stem and the drive rod jointly correspond to the shank 3a shown in FIG. 1.
The electromagnetic valve unit shown in FIG. 1 has electromagnets 5, 6 positioned respectively above and below the armature 4 and having respective solenoids 5a, 6a. The electromagnet 5 serves as a valve-closing electromagnet which, when the solenoid 5a is energized, generates electromagnetic forces to lift and attract the armature 4 thereby to move the valve head 3 into the closed position. The electromagnet 6 serves as a valve-opening electromagnet which, when the solenoid 6a is energized, generates electromagnetic forces to lower and attract the armature 4 thereby to move the valve head 3 into the open position.
The electromagnetic valve unit also has a spring 7 positioned above the armature 4 for normally urging the armature 4 to lower the valve head 3 toward the open position, and a spring 8 positioned below the armature 4 for normally urging the armature 4 to lift the valve head 3 toward the closed position. When the electromagnets 5, 6 are de-energized, the biasing forces of the springs 7, 8 are kept in equilibrium to hold the valve head 3 in a neutral position, indicated by the solid lines, between the closed and open positions. Therefore, the springs 7, 8 jointly serve as a biasing means for biasing the valve head 3 in the neutral position.
For opening the valve head 3 from the closed position in which the armature 4 is attracted to the valve-closing electromagnet 5 under its electromagnetic forces, the solenoid 5a of the valve-closing electromagnet 5 is de-energized to release the armature 4 from the valve-closing electromagnet 5, allowing the valve head 3 to move from the closed position toward the open position under the combined biasing forces of the springs 7, 8. On the movement of the valve head 3 from the closed position toward the open position, the solenoid 6a of the valve-opening electromagnet 6 are energized to attract the armature 4 until the valve head 3 reaches the open position, whereupon the valve head 3 is maintained in the open position.
For moving the valve head 3 from the open position toward the closed position, the solenoid 6a is de-energized to release the armature 4 from the valve-opening electromagnet 6. Thereafter, the solenoid 5a is energized to attract the armature 4 against the valve-closing electromagnet 5. In this manner, the valve head 3 is displaced from the open position into the closed position, and held in the closed position.
The above cycle of opening and closing the valve head 3 is periodically performed in synchronism with the rotational speed of the internal combustion engine.
In order to introduce intake air into and discharge exhaust gases from the combustion chamber 1 smoothly for efficiently operating the internal combustion engine, it is necessary to open and close the valve head 3 such that the displaced position of the valve head 3 between the closed and open positions changes in a desired time-dependent pattern according to the rotational speed of the internal combustion engine. If the opening and closing action of the valve head 3 suffers a difficulty for some reason, such a faulty situation needs to be recognized properly and the valve head 3 needs to be operated for the purpose of avoiding the trouble.
It has been customary for the electromagnetic valve unit to incorporate a displacement sensor for detecting the displaced position of the valve head 3, and to control the energization of the valve-closing electromagnet 5 and the valve-opening electromagnet 6 depending on the displaced position of the valve head 3 as detected by the displacement sensor. The displaced position of the valve head 3 is recognized by comparing the output from the displacement sensor with a predetermined threshold.
Output characteristics of the displacement sensor with respect to the displaced position of the valve head 3 tend to vary from displacement sensor to displacement sensor and also tend to change due to aging. For these reasons, when the output from the displacement sensor is compared with a fixed threshold, the displaced position of the valve head 3 as recognized based on the comparison is liable to vary. As a result, it is difficult to control the energization of the valve-closing electromagnet 5 and the valve-opening electromagnet 6 in order to open and close the valve head 3 accurately and reliably irrespectively of individual internal combustion engines or the period in which the individual internal combustion engine has been used. It is also difficult to appropriately recognize a failure of the opening and closing action of the valve head 3 and adequately operate the valve head 3 depending on the recognized opening and closing action thereof.
Even if the output of the displacement sensor is highly accurate, the opening and closing action of the valve head 3 is affected by the friction of various related parts, the combustion pressure in the combustion chamber 1, different characteristics of the springs 7, 8, and their time-dependent changes. Consequently, if the energization of the valve-closing electromagnet 5 and the valve-opening electromagnet 6 is controlled in a fixed pattern depending on the output of the displacement sensor, then it is difficult to control the opening and closing action of the valve head 3 accurately and stably.
It is therefore an object of the present invention to provide a method of controlling an electromagnetic valve unit for use in internal combustion engines by appropriately performing a process of controlling the energization of a valve-closing electromagnet or a valve-opening electromagnet to open and close a valve head while compensating for variations of the output of a displacement sensor and variations of the friction of various related parts, for thereby opening and closing the valve head accurately and stably.
According to an aspect of the present invention, there is provided a method of controlling an electromagnetic valve unit in an internal combustion engine, having a valve head reciprocally movable between an open position for opening an intake or exhaust port of a combustion chamber in the internal combustion engine and a closed position for closing the intake or exhaust port, biasing means for biasing the valve head to a neutral position between the open position and the closed position, a valve-opening electromagnet for displacing the valve head into the open position under electromagnetic forces, a valve-closing electromagnet for displacing the valve head into the closed position under electromagnetic forces, and a displacement sensor for generating an output depending on a displaced position of the valve head, the method comprising the steps of determining a difference between the output of the displacement sensor when the valve head is in the open position and the output of the displacement sensor when the valve head is in the closed position in each period of an opening and closing action of the valve head, the difference corresponding to a full displacement of the valve head between the open position and the closed position, and establishing, using the difference, a threshold for the output of the displacement sensor which corresponds to a predetermined displaced position of the valve head which is determined based on a proportion of the full displacement, and controlling energization of the valve-opening electromagnet and/or the valve-closing electromagnet depending on whether the output of the displacement sensor has reached the threshold or not upon the opening and closing action of the valve head immediately after the threshold is established.
In the above method, the difference between the output of the displacement sensor when the valve head is in the open position and the output of the displacement sensor when the valve head is in the closed position is determined in each period of an opening and closing action of the valve head. The predetermined displaced position of the valve head for performing energization of the valve-opening electromagnet and the valve-closing electromagnet is determined based on a proportion of the full displacement, and a threshold for the output of the displacement sensor which corresponds to the displaced position is determined using the difference between the outputs of the displacement sensor.
Since the full displacement of the valve head between the open and closed positions corresponds to the difference between the outputs of the displacement sensor, the threshold for the output of the displacement sensor which corresponds to the displaced position determined by the proportion of the full displacement is determined by the proportion according to a proportional distribution. If the displaced position of the valve head is determined as a position displaced from the closed or open position by X % of the full displacement, then the threshold for the output of the displacement sensor is determined as a value which is changed, by X % of the difference, from the output of the displacement sensor when the valve head is in the closed position or the output of the displacement sensor when the valve head is in the open position.
The threshold thus established for the output of the displacement sensor depends on the output characteristics of individual displacement sensors and the output characteristics of the displacement sensor as they vary from time to time. Therefore, the threshold for the output of the displacement sensor which corresponds to the displaced position of the valve head can appropriately be established irrespectively of variations in the output characteristics of the displacement sensor and time-dependent changes therein.
In the above method, energization of the valve-opening electromagnet and/or the valve-closing electromagnet is controlled depending on whether the output of the displacement sensor has reached the threshold or not upon the opening and closing action of the valve head immediately after the threshold is established. Inasmuch as the threshold corresponds to the displaced position of the valve head, energization of the valve-opening electromagnet and/or the valve-closing electromagnet can be controlled at a desired displaced position of the valve head. As a result, the valve head can appropriately be opened and closed as desired.
Therefore, energization of the valve-opening electromagnet and/or the valve-closing electromagnet can be controlled while compensating for variations in the output of the displacement sensor, and hence the valve head can accurately be opened and closed.
The difference between the outputs of the displacement sensor can be determined using only the outputs of the displacement sensor in one period of the opening and closing action of the valve head for establishing the threshold. Preferably, however, the difference comprises a difference between an average value of outputs of the displacement sensor when the valve head is in the open position over a plurality of periods of the opening and closing action of the valve head and an average value of outputs of the displacement sensor when the valve head is in the closed position over a plurality of periods of the opening and closing action of the valve head.
In this manner, the effect of a noise component which may temporarily be contained in the output of the displacement sensor can be compensated for, and hence the difference is made highly reliable. The threshold for the output of the displacement sensor which corresponds to the displaced position of the valve head is also made reliable.
The threshold may include a first threshold corresponding to a position of the valve head which is displaced from one of the open position and the closed position by a first proportion of the full displacement, and the step of controlling energization of the valve-opening electromagnet and/or the valve-closing electromagnet may comprise the steps of measuring a time after the valve-closing electromagnet is de-energized until the output of the displacement sensor reaches the first threshold when the valve head is opened from the closed position, and adjusting a timing to de-energize the valve-closing electromagnet when the valve head is to be opened next time, depending on the measured time.
The threshold may also include a second threshold corresponding to a position of the valve head which is displaced from one of the open position and the closed position by a second proportion of the full displacement, and the step of controlling energization of the valve-opening electromagnet and/or the valve-closing electromagnet may comprise the steps of measuring a time after the valve-opening electromagnet is de-energized until the output of the displacement sensor reaches the second threshold when the valve head is closed from the open position, and adjusting a timing to de-energize the valve-opening electromagnet when the valve head is to be closed next time, depending on the measured time.
The valve head starts being opened from the closed position or closed from the open position when the valve-closing electromagnet and the valve-opening electromagnet are de-energized. To cause the timings to open and close the valve head to match the operating state of the internal combustion engine, it is important to determine a time for the valve head to move to a certain displaced position after the valve-closing electromagnet or the valve-opening electromagnet is de-energized. Such a time, however, tends to vary because of various factors including the friction of various related parts, the characteristics of the biasing means, the internal pressure (combustion pressure) in the combustion chamber, and remaining magnetic forces immediately after the electromagnets are de-energized.
According to the invention, for opening the valve head, a time after the valve-closing electromagnet is de-energized until the output of the displacement sensor reaches the first threshold is measured when the valve head is opened from the closed position, and a timing to de-energize the valve-closing electromagnet when the valve head is to be opened next time is adjusted depending on the measured time. For closing the valve head, a time after the valve-opening electromagnet is de-energized until the output of the displacement sensor reaches the second threshold is measured when the valve head is closed from the open position, and a timing to de-energize the valve-opening electromagnet when the valve head is to be closed next time is adjusted depending on the measured time.
It is thus possible to adjust the above time to a desired time while compensating for the friction of various related parts, variations in the characteristics of the biasing means, etc. Since the first or second threshold is established as described above, the measured time accurately agrees with the time required after the valve-closing electromagnet or the valve-opening electromagnet is de-energized until the valve head actually moves to the displaced position. Consequently, when the timing to de-energize the valve-closing electromagnet and the valve-opening electromagnet is adjusted depending on the measured time, it is possible to control the timing for the valve head to the displaced position reliably at a desired timing.
The threshold may include a third threshold corresponding to a position of the valve head which is displaced from one of the open position and the closed position by a third proportion of the full displacement, and a fourth threshold corresponding to a position of the valve head which is closer to the open position than the position corresponding to said third position and displaced from one of the open position and the closed position by a fourth proportion of the full displacement, and the step of controlling energization of the valve-opening electromagnet and/or the valve-closing electromagnet may comprise the steps of measuring a time after the output of the displacement sensor reaches the third threshold until the output of the displacement sensor reaches the fourth threshold when the valve head is opened from the closed position, and adjusting a timing to energize the valve-opening electromagnet when the valve head is to be opened next time, depending on the measured time.
Furthermore, the threshold may include a fifth threshold corresponding to a position of the valve head which is displaced from one of the open position and the closed position by a fifth proportion of the full displacement, and a sixth threshold corresponding to a position of the valve head which is closer to the closed position than the position corresponding to the fifth proportion and displaced from one of the open position and the closed position by a sixth proportion of the full displacement, and the step of controlling energization of the valve-opening electromagnet and/or the valve-closing electromagnet may comprise the steps of measuring a time after the output of the displacement sensor reaches the fifth threshold until the output of the displacement sensor reaches the sixth threshold when the valve head is closed from the open position, and adjusting a timing to energize the valve-opening electromagnet when the valve head is to be closed next time, depending on the measured time.
To cause the opening and closing action of the valve head to match the operating state of the internal combustion engine, it is important to determine a speed at which the valve head moves from the closed position to the open position and a speed at which the valve head moves from the open position to the closed position. However, those speeds are liable to vary because of various factors including the friction of various related parts, the characteristics of the biasing means, the internal pressure (combustion pressure) in the combustion chamber, and remaining magnetic forces immediately after the electromagnets are de-energized. For opening the valve head, the above speed can be controlled by the timing to energize the valve-opening electromagnet, and for closing the valve head, the above speed can be controlled by the timing to energize the valve-closing electromagnet.
According to the present invention, as described above, for opening the valve head, a time after the output of the displacement sensor reaches the third threshold until the output of the displacement sensor reaches the fourth threshold is measured when the valve head is opened from the closed position, and a timing to energize the valve-opening electromagnet when the valve head is to be opened next time is adjusted depending on the measured time. For closing the valve head, a time after the output of the displacement sensor reaches the fifth threshold until the output of the displacement sensor reaches the sixth threshold is measured when the valve head is closed from the open position, and a timing to energize the valve-opening electromagnet when the valve head is to be closed next time is adjusted depending on the measured time. Since the third through sixth thresholds are established as described above, the output of the displacement sensor in the displaced position of the valve head is highly reliable. The measured times are also highly reliable as representing the actual speed of the valve head.
Therefore, the speed of the valve head as it is opened or closed can be controlled accurately at a desired speed while compensating for the friction of various related parts, etc.
The threshold may include a seventh threshold corresponding to a position of the valve head which is close to the open position and displaced from one of the open position and the closed position by a seventh proportion of the full displacement, and the step of controlling energization of the valve-opening electromagnet and/or the valve-closing electromagnet may comprise the steps of energizing the valve-opening electromagnet in a constant-voltage control mode after the valve-opening electromagnet starts being energized until the output of the displacement sensor reaches the seventh threshold when the valve head is opened from the closed position, and energizing the valve-opening electromagnet in a constant-current control mode after the output of the displacement sensor reaches the seventh threshold.
The threshold may include an eighth threshold corresponding to a position of the valve head which is close to the closed position and displaced from one of the open position and the closed position by an eighth proportion of the full displacement, and the step of controlling energization of the valve-opening electromagnet and/or the valve-closing electromagnet may comprise the steps of energizing the valve-closing electromagnet in a constant-voltage control mode after the valve-closing electromagnet starts being energized until the output of the displacement sensor reaches the eighth threshold when the valve head is closed from the open position, and energizing the valve-closing electromagnet in a constant-current control mode after the output of the displacement sensor reaches the eighth threshold.
For opening the valve head, until the valve head reaches a position close to the open position, the valve-opening electromagnet is preferably energized in the constant-voltage control mode in which a solenoid of the valve-opening electromagnet is energized under a constant voltage applied thereto. Similarly, the valve-closing electromagnet is preferably energized in the constant-voltage control mode in which a solenoid of the valve-closing electromagnet is energized under a constant voltage applied thereto. The constant-voltage control mode allows the valve head to move quickly to the open or closed position because the current supplied to the electromagnet increases, i.e., electromagnetic forces generated thereby increase, ass the valve head moves. When the valve head moves to a position near the open position at the time it is to be opened or when the valve head moves to a position near the closed position at the time it is to be closed, the valve-opening electromagnet or the valve-closing electromagnet is preferably energized in the constant-current control mode in which the solenoid of the electromagnet is energized with a constant current supplied thereto. Particularly after the valve head has reached the open or closed position, the valve head is preferably held in that position in the constant-current control mode because electromagnetic forces required to hold the valve head in the position may be relatively small.
According to the present invention, as described above, for opening the valve head, the valve-opening electromagnet is energized in the constant-voltage control mode after the valve-opening electromagnet starts being energized until the output of the displacement sensor reaches the seventh threshold corresponding to the position in the vicinity of the open position, and the valve-opening electromagnet is energized in the constant-current control mode after the output of the displacement sensor reaches the seventh threshold. For closing the valve head, the valve-closing electromagnet is energized in the constant-voltage control mode after the valve-closing electromagnet starts being energized until the output of the displacement sensor reaches the eighth threshold corresponding to the position in the vicinity of the closed position, and the valve-closing electromagnet is energized in the constant-current control mode after the output of the displacement sensor reaches the eighth threshold.
When the valve head is opened, the valve head can smoothly be moved to the open position, smoothly reach the open position, and smoothly be held in the open position. Similarly, when the valve head is closed, the valve head can smoothly be moved to the closed position, smoothly reach the closed position, and smoothly be held in the closed position. Inasmuch as the seventh or eighth threshold for determining the timing to change from the constant-voltage control mode to the constant-current control mode is determined as described above, the energization of the electromagnets can be switched between these control modes at a desired displaced position of the valve head near the open or closed position without being affected by variations in the output characteristics of the displacement sensor, etc. Thus, the valve head can stably and smoothly be opened and closed regardless of variations in the output characteristics of the displacement sensor, etc. Because the timing to change from the constant-voltage control mode to the constant-current control mode determined by the seventh or eighth threshold is highly reliable, the electric energy supplied to the electromagnets is minimized, and hence the power consumption by the electromagnets is reduced.
The threshold may include a ninth threshold corresponding to a position of the valve head which is close to the open position and displaced from one of the open position and the closed position by a ninth proportion of the full displacement, and the step of controlling energization of the valve-opening electromagnet and/or the valve-closing electromagnet may comprise the step of performing a first failure process to control energization of the valve-opening electromagnet and/or the valve-closing electromagnet if the output of the displacement sensor has not reached the ninth threshold at a predetermined timing when the valve head is opened from the closed position.
The threshold may include a tenth threshold corresponding to a position of the valve head which is close to the closed position and displaced from one of the open position and the closed position by a tenth proportion of the full displacement, and the step of controlling energization of the valve-opening electromagnet and/or the valve-closing electromagnet comprises the step of performing a second failure process to control energization of the valve-opening electromagnet and/or the valve-closing electromagnet if the output of the displacement sensor has not reached the tenth threshold at a predetermined timing when the valve head is closed from the open position.
When the valve head is to be opened, if the valve head moves normally from the closed position to the open position, then the valve head reaches a certain displaced position or a position closer to the open position than the displaced position at a certain timing, e.g., when a certain time has elapsed after the valve-closing electromagnet is de-energized. Similarly, when the valve head is to be closed, if the valve head moves normally from the open position to the closed position, then the valve head reaches a certain displaced position or a position closer to the closed position than the displaced position at a certain timing, e.g., when a certain time has elapsed after the valve-opening electromagnet is de-energized. If the valve head has not reached such a position at the above timing, then the valve head is suffering a certain malfunction.
According to the present invention, as described above, the first failure process is performed to control energization of the valve-opening electromagnet and/or the valve-closing electromagnet if the output of the displacement sensor has not reached the ninth threshold at a predetermined timing when the valve head is opened from the closed position. Likewise, the second failure process is performed to control energization of the valve-opening electromagnet and/or the valve-closing electromagnet if the output of the displacement sensor has not reached the tenth threshold at a predetermined timing when the valve head is closed from the closed position.
Therefore, when the valve head malfunctions as it moves at the time it is opened or closed, it is possible to energize the valve-opening electromagnet or the valve-closing electromagnet in a manner to cope with the malfunction. Since the ninth or tenth threshold is established as described above, it reliably corresponds to the desired displaced position of the valve head in the vicinity of the open or closed position irrespectively of variations in the output characteristics of the displacement sensor, etc. Consequently, only when the valve head malfunctions upon its movement at the time it is opened or closed, the first or second failure process can be carried out to energize the valve-opening electromagnet or the valve-closing electromagnet in a manner to cope with the malfunction.
The first or second failure process may comprise a process of alternately energizing the valve-opening electromagnet and the valve-closing electromagnet in predetermined periods until the valve head reaches either one of the valve-opening electromagnet and the valve-closing electromagnet.
By thus alternately energizing the valve-opening electromagnet and the valve-closing electromagnet in predetermined periods, the valve head is vibrated between the open and closed positions, and can be moved to one of the open and closed positions due to reduced resonance. When the valve head is moved to one of the open and closed positions, the valve head can then resume its normal opening and closing action from that position.
The threshold may include an eleventh threshold corresponding to a position of the valve head which is close to the open position and displaced from one of the open position and the closed position by an eleventh proportion of the full displacement, and the step of controlling energization of the valve-opening electromagnet and/or the valve-closing electromagnet may comprise the step of performing a third failure process to control energization of the valve-opening electromagnet and/or the valve-closing electromagnet when the output of the displacement sensor has changed to the eleventh threshold before the valve-opening electromagnet is de-energized, after the valve head is displaced from the closed position to the open position.
The threshold may include a twelfth threshold corresponding to a position of the valve head which is close to the closed position and displaced from one of the open position and the closed position by a twelfth proportion of the full displacement, and the step of controlling energization of the valve-opening electromagnet and/or the valve-closing electromagnet may comprise the step of performing a fourth failure process to control energization of the valve-opening electromagnet and/or the valve-closing electromagnet when the output of the displacement sensor has changed to the twelfth threshold before the valve-closing electromagnet is de-energized, after the valve head is displaced from the open position to the closed position.
After the valve head has reached the open position, if the valve head is displaced toward the closed position to a position in the vicinity of the open position, then the valve head suffers a certain malfunction. similarly, after the valve head has reached the closed position, if the valve head is displaced toward the open position to a position in the vicinity of the closed position, then the valve head suffers a certain malfunction.
According to the present invention, as described above, after the valve head is displaced from the closed position to the open position, the third failure process is performed to control energization of the valve-opening electromagnet and/or the valve-closing electromagnet when the output of the displacement sensor has changed to the eleventh threshold before the valve-opening electromagnet is de-energized. Likewise, after the valve head is displaced from the open position to the closed position, the fourth failure process is performed to control energization of the valve-opening electromagnet and/or the valve-closing electromagnet when the output of the displacement sensor has changed to the twelfth threshold before the valve-closing electromagnet is de-energized.
In this manner, when the valve head cannot be held in the open or closed position due to a malfunction, it is possible to energize the valve-opening electromagnet or the valve-closing electromagnet in a manner to cope with the malfunction. Inasmuch as the eleventh and twelfth thresholds are established as described above, they reliably correspond to the desired displaced position of the valve head for determining whether the third and fourth failure processes are to be performed or not, irrespectively of variations in the output characteristics of the displacement sensor, etc. Consequently, only when the valve head malfunctions and fails to be held in the open or closed position, the third or fourth failure process can be carried out to energize the valve-opening electromagnet or the valve-closing electromagnet in a manner to cope with the malfunction.
The third failure process may comprise a process of deciding whether the valve head can be returned to the open position by energizing the valve-opening electromagnet within a period up to a timing to de-energize the valve-opening electromagnet in order to close the valve head, energizing the valve-opening electromagnet to return the valve head to the open position if the valve head can be returned to the open position within the period, de-energizing the valve-opening electromagnet if the valve head cannot be returned to the open position within the period, and energizing the valve-closing electromagnet to move the valve head to the closed position at a predetermined timing.
The fourth failure process may comprise a process of deciding whether the valve head can be returned to the closed position by energizing the valve-closing electromagnet within a period up to a timing to de-energize the valve-closing electromagnet in order to open the valve head, energizing the valve-closing electromagnet to return the valve head to the closed position if the valve head can be returned to the closed position within the period, de-energizing the valve-closing electromagnet if the valve head cannot be returned to the closed position within the period, and energizing the valve-opening electromagnet to move the valve head to the open position at a predetermined timing.
By thus controlling energization of the valve-opening electromagnet and the valve-closing electromagnet, the normal opening and closing action of the valve head can be recovered without impairing the operating state of the internal combustion engine.
The first through twelfth thresholds described above may be different from each other, or some of the first through twelfth thresholds may be identical to each other.
According to another aspect of the present invention, there is provided a method of controlling an electromagnetic valve unit in an internal combustion engine, having a valve head reciprocally movable between an open position for opening an intake or exhaust port of a combustion chamber in the internal combustion engine and a closed position for closing the intake or exhaust port, biasing means for biasing the valve head to a neutral position between the open position and the closed position, a valve-opening electromagnet for displacing the valve head into the open position under electromagnetic forces, a valve-closing electromagnet for displacing the valve head into the closed position under electromagnetic forces, and a displacement sensor for generating an output depending on a displaced position of the valve head, the method comprising the steps of determining a first threshold for the output of the displacement sensor which corresponds to a position of the valve head which is displaced from one of the open position and the closed position by a first distance and a second threshold for the output of the displacement sensor which is closer to the open position than the position corresponding to the first distance and displaced from one of the open position and the closed position by a second distance, measuring a time after the output of the displacement sensor has reached the first threshold until the output of the displacement sensor reaches the second threshold when the valve head is opened from the closed position, and adjusting a timing to energize the valve-opening electromagnet when the valve head is to be opened next time, depending on the measured time.
According to still another aspect of the present invention, there is provided a method of controlling an electromagnetic valve unit in an internal combustion engine, having a valve head reciprocally movable between an open position for opening an intake or exhaust port of a combustion chamber in the internal combustion engine and a closed position for closing the intake or exhaust port, biasing means for biasing the valve head to a neutral position between the open position and the closed position, a valve-opening electromagnet for displacing the valve head into the open position under electromagnetic forces, a valve-closing electromagnet for displacing the valve head into the closed position under electromagnetic forces, and a displacement sensor for generating an output depending on a displaced position of the valve head, the method comprising the steps of determining a third threshold for the output of the displacement sensor which corresponds to a position of the valve head which is displaced from one of the open position and the closed position by a third distance and a fourth threshold for the output of the displacement sensor which is closer to the closed position than the position corresponding to the third distance and displaced from one of the open position and the closed position by a fourth distance, measuring a time after the output of the displacement sensor has reached the third threshold until the output of the displacement sensor reaches the fourth threshold when the valve head is closed from the open position, and adjusting a timing to energize the valve-closing electromagnet when the valve head is to be closed next time, depending on the measured time.
In the above two latter methods, two thresholds, i.e., the first and second threshold or the third and fourth thresholds, for the output of the displacement sensor are determined as corresponding to two displaced positions between the open and closed positions. When the valve head is to be opened or closed, a time required after the output of the displacement sensor has reached one of the thresholds until the output of the displacement sensor reaches the other threshold is measured. The measured time corresponds to a speed of the valve head as it is opened or closed. The timing to energize the valve-opening electromagnet to open the valve head next time or the timing to energize the valve-closing electromagnet to close the valve head next time is adjusted depending on the measured time.
As a consequence, the speed at which the valve head moves when it is opened or closed can be controlled accurately at a desired speed while compensating for the friction of various related parts, the characteristics of the biasing means, the internal pressure (combustion pressure) in the combustion chamber, and remaining magnetic forces immediately after the electromagnets are de-energized.
The above two latter methods can be carried out simultaneously in combination with each other.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.